This invention relates to a novel curable copolymer of chlorotrifluoroethylene, a fatty acid ester and a hydroxyl-containing allyl ether and also to a coating liquid composition using the novel copolymer.
Polymers of some fluoro compounds have provided synthetic resins which have good mechanical properties and are superior in heat resistance, chemical resistance and weather resistance. As one field of wide applications of fluorine-containing polymers or fluoro-resins, progressive development has been made in the use of fluoro-resins as paint vehicles with a view to utilizing their excellent chemical resistance and weather resistance for producing maintenance-free coatings. For example, polytetrafluoroethylene, polychlorotrifluoroethylene and copolymers of vinylidene fluoride have attracted interest for this purpose, and also it has been developed to modify a conventional synthetic resin base paint by the addition of a certain fluoro-resin.
In the early days of the development fluoro-resin base paints were almost limited to powder paints and dispersions in water or organic liquid, and these paints require high temperature baking finish which calls for skill and should be performed by experts. To expand practical applicabilities of fluoro-resin base paints, recently much attention has been directed to fluoro-resin base paints of the solvent-thinned type which do not require baking finish and, therefore, can easily be used on the site of mechanical manufacturing or building work.
To obtain fluoro-resins that are soluble in practicable organic solvents and useful as vehicles in solvent-thinned paints, usually it is necessary to reduce crystallinity of fluorine-containing polymers by certain means such as copolymerization to thereby accomplish internal plasticization. Furthermore, there are some problems to be settled in producing a practical paint by using a fluoro-resin which is rendered soluble. For instance, the problems will be how to retain a desirable degree of rigidity or shear modulus in the soluble fluoro-resin, how to control the molecular weight of the fluoro-resin with a view to desirably adjusting the viscosity of the paint and how to select and control the kind and amount of functional groups which must be introduced into the soluble fluoro-resin in order to obtain a paint that is curable and accordingly is recoatable. Cost of production also has to be taken into consideration. It is not always easy to reach balanced solutions for all of these problems.
It is reported in British patent No. 888,014 and in J. Polymer Science, 11, No. 5, 455 (1953) that a copolymer of chlorotrifluoroethylene with a vinyl ester of fatty acid exhibits high transparency over a wide range of wavelength and possesses high tensile strength and excellent impact resistance and can relatively easily be dissolved in organic solvents by moderate heating. If a solution of this copolymer is used as a paint or coating composition it is possible to obtain a coating film that is hard, transparent and glossy. However, this solution lacks recoatability since the copolymer is not curable.